Foam spray guns of the type disclosed herein have been used for many applications, including for example, by the construction industry to provide thermal insulation, sound attenuation, etc. Foam application apparatus are commercially available for applying two-component foamable fluid plastic resins, including polyurethanes. Such foam application apparatus may include a cylindrical mixing chamber having separate inlet passages for each component and an axial outlet passage, and the apparatus generally includes a reciprocal valve rod having a free end. The free end of the valve rod reciprocates in the mixing chamber from an "off" position, wherein the valve rod free end blocks the inlet passages, to an "on" position, wherein the rod is retracted in the chamber to permit free communication between the inlet and outlet passages.
The automotive industry utilizes insulation for sound attenuation or deadening and as a thermal insulator. Foamed plastic resins are not generally used for such applications by the automotive industry, although the desire for weight reduction and the use of thinner body panels and plastic fascia makes use of such foam resins attractive. The mass production techniques used by the automotive industry, however, require reliability over tens of thousands of applications. Conventional foam application guns commonly seize up after a few thousand shots, requiring cleaning of the valve components before reuse. Another problem with conventional commercially available two-component foam application guns is leakage of fluid resin, particularly through the nozzle, when the gun is turned off or not in use. Various seals have been used to reduce leakage of foam application guns, including providing a single radial groove in the valve rod adjacent the free end. Fluid resin fills the groove to provide an O-ring-type seal, which is replenished as the rod reciprocates in the mixing chamber.
The attempts to solve these problems with conventional foam application guns for mass-production applications have not, however, been commercially successful. The need therefore remains for a more reliable foam application apparatus, particularly for applying two-component foamable fluid resins, for mass production applications. The foam application gun must be able to operate for tens of thousands of applications, without seizure, and the gun should not leak between applications. The apparatus for applying a two-component foamable fluid plastic resin of this invention solves these problems in a relatively simple manner, and is suitable for mass production applications.